This invention relates to nickel base superalloys and, more particularly, to such alloys for use as single crystal articles at elevated temperatures of about 2000.degree. F. and above.
A number of high temperature nickel base superalloys have been developed and reported for use in the form of single crystal articles at high temperature under severe Icad conditions. For example, such conditions exist in the turbine section of advanced gas turbine engines for aircraft use. Such single crystal articles are useful as airfoils in these turbine sections.
In general, the recent advances in alloy strength for single crystal articles useful at such high temperatures and severe Icad conditions have been accomplished by the incorporation of "heavy" refractory elements into the alloy, which inhibit the atomic diffusion process. These refractory elements include rhenium (Re), tungsten (W), tantalum (Ta), and molybdenum (Mo). Unfortunately these alloying additions of rhenium, tungsten, molybdenum and tantalum cannot be made to strengthen such nickel base superalloy articles without rendering the alloy more susceptible to the precipitation of undesirable phases. Especially detrimental are phases known as the topologically close packed (TCP) phases which form after exposure at temperatures above about 1800.degree. F. TCP phases are not only brittle, but their formation reduces solution strengthening potential of the alloy by removing solute elements from the desired alloy phases and concentrating them in the brittle phases so that intended strength and life goals are not met.